Coinfection with HIV and HCV is a rapidly growing public health issue. HIV/HCV coinfection is common in injection drug users (IDUs), the single largest group for HCV infection in the USA. HCV coinfection is becoming even more significant, as HIV-infected people are living longer with HAART. However, we have limited and conflicting information about the interactions between opioids, host innate immunity and HIV/HCV. Importantly, no study to date has addressed combined effects of heroin use and HCV on HIV infection as well as on TLR3/RIG-I-mediated innate immunity, which is a major barrier of fundamental understanding of the immunopathogenesis of HIV disease in HIV and/or HCV-infected IDUs. The goal of this proposal is to address our overarching hypothesis that the negative impact of opioids (heroin, morphine) on the antiviral innate immunity is crucial in facilitating HIV or HCV infection. We will investigate the impact of heroin use and/or HCV on host innate immunity and HIV/HCV infection. We will determine previously unrecognized mechanisms by which opioids compromise TLR3/RIG-I (the key sensors of viral infection)-mediated innate immunity against HIV/HCV infection. We propose the following specific aims: Aim 1. Determine in vivo impact of heroin and/or HCV infection on plasma and PBMC levels of HIV, CD4 T cell counts and antiviral cellular factors related to HIV or HCV infection; Aim 2. Determine the ex vivo effects of heroin and/or HIV/HCV infection on the activation of TLR3/RIG-I signaling pathways; Aim 3. Determine the mechanism(s) by which morphine and/or HIV/HCV infection compromise TLR3/RIG-I signaling- mediated anti-HIV/HCV effects in primary macrophages and hepatocytes. Data arising from this study using the specimens from the unique Chinese heroin-dependent subjects with or without HIV and/or HCV infection will be clinically relevant and important in our understanding of the in vivo interplays between opioids, host innate immunity and viral infections. Long term goal of this project is to develop host innate immunity-based treatment and prevention strategies for HIV/HCV-infected opioid-abusers.